Networks are electronic systems that include server stations that couple information to one or more client/slave stations. When a server is first turned on, e.g., when electrical power is first applied, it is important to first power server units such as the central processing system ("CPU"), often referred to as a "card cage", and then provide power to ancillary systems, including memory units. It is the function of an AC sequencer to ensure that server power-up applies power to server units in a correct sequence. For example, if power were simultaneously and instantly applied to all units within the server, the in-rush of current would almost certainly trip circuit breakers associated with the source of AC power into the sequencer.
FIG. 1A shows a prior art network system 10 such as might be used in the United States. System 10 includes a server 20 and a client/slave 30, each of which is mounted in a cabinet or relay-type rack 40. Rack 40 commonly measures perhaps 142 cm in height, and about 56 cm in width and depth. Source AC power to units 20 and 30 is received via a power cord 50 whose free end is connected to an AC connector 60 sized to fit into an AC wall outlet receptacle 70. As well be described, the other end of power cord 50 is hardwired to an AC sequencer unit 80 within rack 40. Typically source AC power is about 210 VAC to 240 VAC, 50 Hz to 60 Hz, 30 A maximum.
Each unit 20, 30 includes an AC sequencer 80 that receives source AC via hardwired power cord 50, and sequentially provides AC operating power to other units within unit 20 or unit 30. Because unit 20 is a server unit 20, it will include a central processing unit card ("CPU") 90, which card is not present in slave unit 30. As shown in FIG. 1A, present in unit 20 and slave unit 30 are a fan tray 100 for cooling the unit, and storage or memory trays, shown as 110A, 110B, 110C, etc. The storage units may include perhaps six hard disk drive assemblies, compact disk ("CD") assemblies, optical disk assemblies, and magnetic tape drives. Client/slave unit 40 is shown with a further memory unit, memory tray 110C, that has been plugged into cabinet 30 in lieu of a CPU card tray 80. In this fashion, unit 30 is able to provide additional storage capability by allowing three rather than two trays for memory assemblies.
If AC operating power were simultaneously provided to unit 20 and unit 30 at power-up, the resultant current surge could exceed the current limit of protective circuit breakers within each AC sequencer unit. Further, simultaneous receipt of AC operating power by CPU tray 90 and various associated memory trays, e.g., 110A, 110B, could result in inoperative starting states for the master unit 20. Thus, a function of AC sequencer 80 is to receive raw AC power from wall socket 70, and to sequentially provide operating power to other units within the same rack 40.
More specifically, each AC sequencer 80 typically outputs AC operating voltage to three power output ports.
A first outlet port 120 provides the "unswitched" AC voltage as soon as operating voltage is coupled to the AC sequencer. A second outlet port 130 provides a "switched 1" AC voltage, which is defined as a voltage which is applied only after application of a POWER-ON switch closure control signal to port 135-IN. A third outlet port 140 provides a "switched 2" AC voltage which is defined as a voltage which is applied only after a delay time of about four to six seconds from occurrence of the "switched 1" AC power.
The connection between each AC sequencer 80 and control input port 135-IN is hardwired to the AC sequencer. Further, each AC sequencer outputs control signals through an output control port 135-OUT. These control signals may be coupled via a cable 155 to the input control port 135-IN of another unit 30, as shown in FIG. 1A.
System 10 in FIG. 1A is intended for use in the United States. As such, wall connector 70, AC connector plug 60 and power cord 50 (among other components) must satisfy Underwriter Laboratories ("UL") standards that apply to electrical equipment used in the United States. For example, the diameter and number of wires within the power cord 50 and the dimensions and configuration of the AC connector plug 60 will be governed by applicable UL standards.
However, electrical power standards differ from country to country. Thus, although network systems, servers and client/slaves are commonly used world-wide, manufacturers of AC sequencers have had to manufacture different sequencer versions for different countries. For example, FIG. 1B depicts a system 10' such as might be used in Europe or in another country whose electrical power standards do not conform to UL standards.
Among other changes, wall-mounted AC outlet receptacle 70' will have a different configuration than a U.L. approved receptacle 70. Because applicable standards differ, AC plug 60', and AC power cord 50' will be different, and AC connector 60', and indeed sequencer 80' must thus be changed for system 10' from what was manufactured for system 10.
Unfortunately, standards applicable in various foreign countries preclude providing AC sequencer 80' with multiple AC power cords 50' and AC connector 60'. Such standards also preclude providing differently shaped connectors on the AC sequencer, into one of which a suitable AC power cord could be plugged, rather than hard-wire the AC power cord to the AC sequencer. The other end of such an AC power cord could otherwise have attached an AC connector plug appropriate for the country in which the sequencer was to be used.
The inability of prior art AC sequencers 80, 80' to conform to applicable electrical power and connector standards in all major countries adds to the manufacturing cost that a "family" of sequencers must be produced. Stated differently, if a single AC sequencer could be designed for use world-wide, the cost to produce and indeed maintain the sequencer would be reduced.
Prior art AC sequencers such as shown in FIGS. 1A and 1B suffer an additional deficiency in that often there is a need for more resources than can be supported in a single cabinet rack 40. For example, server 20 may require more storage capacity than can be accommodated using only memory trays 110A, 110B, yet there are no additional tray spaces to receive additional memory. One solution might be to daisy-chain server 20 with a slave 30 using cable 155 and associated connectors. This might provide server 20 with more resources, for example, three additional trays of memory within cabinet 30. In such an application, unit 30 would not be a client per se, but rather a slave that provides additional resources to master unit 20.
Unfortunately, such daisy-chaining is not readily implemented using prior art AC sequencers because there is not a universally accepted connector for the control input/output signals 135-IN, 135-OUT. A second impediment to such daisy-chaining is that the control signals presented at 135-IN could only be switch openings or closures (e.g., a 0 .OMEGA. or .infin..OMEGA. condition). If the control could also accept voltage or current source signals, it would be possible to couple slave sequencers to master sequencers such that full control and status information with respect to the slave unit was available at the server unit.
Thus, there is a need for an AC sequencer to which AC operating power may be coupled in a universal fashion such that a common AC sequencer complies with applicable power standards in all major countries of the world. Further, such an AC sequencer should include a universally acceptable control input and output port that can respond not only to a switch closure, but to a voltage source signal as well as to a current source signal. Finally, such an AC sequencer should also provide indication of the status of units in a slave system coupled to a master system AC sequencer.
The present invention discloses such an AC sequencer.